A conventional inspectable plate heat exchanger comprises a plurality of plates kept tightened and packed together by a plurality of tie rods extending between a pair of side plates having a suitable thickness. More particularly, a plurality of through holes are formed in the two side plates, each through hole in a side plate being aligned, in use, with a respective through hole formed in the other side plate, a respective tie rod being inserted in each pair of aligned holes.
Each plate of the exchanger is suitably shaped, in such a way as to delimit, on one side, a channel extending at the edge of the plate and designed to receive a gasket. The channel has two side sections, substantially parallel with one another, and two sections, one being delimited at the top and the other at the bottom of the plate, which extend in a substantially diagonal direction and are designed to connect the two side sections.
Fluids at a different temperature one with respect to the other are then alternatingly supplied between adjacent pairs of plates, thereby obtaining heat exchange therebetween, whereas the gaskets received in the channels or recesses ensure the seal between the plates.
As it is known, a plate heat exchanger correctly performs its function when the plates are kept packed and pressed together, and the seal gaskets are seated in position, thereby preventing fluid leakages, which, as it will be understood, would cause pressure drops, and thus a decrease in heat exchange efficiency.
It is worth noting that once the plates have been packed together, the side sections of the gaskets in adjacent plates are, as a matter of fact, substantially aligned with one another, whereas this is not the case with the diagonal sections of the same gaskets, which can result in a poorer seal at the upper and lower, in use, portions of the exchanger, i.e. where the seal of the exchanger is obtained by the diagonal sections of the gaskets. It is therefore imperative to be able to suitably compress the gaskets.
It has been evaluated that a collapsed or fluid leakage zone in conventional inspectable plate heat exchangers, more particularly heat exchangers of large size, is usually an intermediate portion between the lower and the upper portion.
Moreover, the two side plates arranged to keep the plate pack tightened have a lower resistance at the intermediate portions of the exchanger.
As it is known, in fact, the two side plates are usually made of carbon steel and have a thickness up to 60 mm or more, as a function of the pressure which they are designed to apply to the exchanger plate pack and of the size of the plate pack. The pair of side plates are tighten by means of tie rods having threaded ends engaged by a respective tightening nut, in such a way as to obtain a degree of tightening or compression for the seal gaskets suitable for preventing, in use, fluid leakages that would result in load losses, i.e. for keeping the fluids flowing through the plate pack at a predetermined operation pressure.
The international application WO-2010/036183 teaches a heat exchanger provided with, among the other things, a side plate having a base plate and a connecting part with an external curved wall extending from an intermediate portion of the base plate. According to such a document, a connection part thus-shaped is intended to provide the side plate with a sufficient space for allowing the heat exchanger connections that, should a flat side plate be used, could not be implemented. In the same document, it is further stated that the base plate can be provided with portions having a greater thickness, thereby withstanding high stress, and the base plate and the connecting part can be obtained by casting, moulding, etc., and thus the connecting part is obtained integral with the base plate.
U.S. Pat. No. 2,379,671 teaches a side plate for heat exchangers, made in one piece that can include a flat internal portion and a substantially curved external portion with concavity facing towards the inside of the exchanger.
The German patent application DE-29 43 010 teaches a heat exchanger provided with a side plate made in one piece and provided with a base plate and external stiffening elements.
The UK patent application GB-2 054 819 teaches a heat exchanger provided with a side plate shaped in such a way as to have external or side sections which are substantially tilted or lowered with respect to an intermediate section.
The UK patent GB-1 364 705 teaches a heat exchanger provided with side plates having a base plate and external stiffening elements welded thereto.